Digital power control system for a multi-carrier transmitter

ABSTRACT

A power control system for a multi-carrier base station transmitter is capable of controlling power levels of individual RF carriers. The power control system has a multi-channel conversion system for generating a plurality of analog reference signals corresponding to a plurality of digital input signals. The multi-channel conversion system also generates an analog multi-carrier signal and samples the multi-carrier signal. The multi-carrier signal represents a summed amplification of the digital input signals. A correlating power detection system is connected to the multi-channel conversion system and generates digital total power control signals based on the analog reference signals and the analog sampled multi-carrier signal. A feedback conversion module is connected to the multi-channel conversion system and the correlating power detection system and individually controls amplification of the digital input signals based on the total power control signals.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to wireless communications. Moreparticularly, the present invention relates to a power control systemfor a multi-carrier base station transmitter, having a correlating powerdetection system for individually controlling the power levels of anarbitrary number of RF carriers.

2. Discussion of the Related Art

Wireless communication systems require the coordination of a number ofdevices such as base stations, controllers, and mobile subscriberequipment. Base stations generally function as an interface between thesubscriber equipment and the controllers in a given network. Therefore,the typical base station must both transmit and receive RF signals toand from the other components of the network.

A particularly challenging requirement of base station transmitters ispower control. For example, in a spread spectrum protocol such as CDMA,a given multi-carrier signal will contain information that issimultaneously transmitted to subscribers that are both near and faraway from the transmitter. In order to avoid significant interferenceproblems throughout the entire coverage area, it is crucial that thepower control system be able to set the power levels of the individualRF carriers to a high level of precision. This requirement is primarilydue to multi-path effects and is well documented in the industry.Conventional systems, however, either have inadequate individual powercontrol, or use elaborate dedicated systems for each RF carrier. It iseasy to understand that the complicated nature of the dedicated systemsapproach significantly increases the costs of the power control systemas well as the overall transmitter. It is therefore desirable to providea power control system for a base station transmitter that uses a sharedsystem to control the power level of individual RF carriers in amulti-carrier system.

Another concern regarding conventional power control systems issaturation. Generally, a typical power control system will have amulti-channel power amplifier that amplifies a summation of theindividual RF carrier signals before transmission. Each RF carriersignal will have a distinct frequency. The resulting plurality offrequencies in the multi-carrier signal leads to distortion and anincrease in the overall power encountered by the multi-channel poweramplifier. If the power levels of the individual carriers are nottightly controlled, the multi-channel power amplifier can be driven intosaturation. The result can be a significant degradation in the receivedsignal.

Conventional systems also fail to adequately address the fact that thetemperature of the power detection system is also directly related tothe ability to control the transmitted power. For example, if an I/Qdetector is used to generate an in phase power signal and a quadraturesignal, the mixing components of the I/Q detector are slightlytemperature dependent. The result may lead to inaccurate powermeasurement and therefore, inaccurate power control. It is thereforehighly desirable to provide a power control system that does not resultin saturation, and is able to account for system temperaturefluctuations.

SUMMARY OF THE INVENTION

The above and other objectives are achieved by an analog-based powercontrol system for a multi-carrier base station transmitter inaccordance with the present invention. The power control system has amulti-channel amplification system for converting a plurality of analoginput signals into a plurality of amplified carrier signals. Theamplification system also generates a plurality of reference signalscorresponding to the amplified carrier signals. Furthermore, theamplification system generates a multi-carrier signal and samples themulti-carrier signal, where the multi-carrier signal includes asummation of the amplified carrier signals. A correlating powerdetection system is connected to the amplification system, and generatestotal power control signals based on the reference signals and thesampled multi-carrier signal. The control system further includes anadjustment module connected to the amplification system and the powerdetection system. The adjustment module controls amplification of thecarrier signals based on the total power control signals.

Further in accordance with the present invention, a digital-based powercontrol system is provided. The power control system includes amulti-channel conversion system, a correlating power detection system,and a feedback conversion module. The multi-channel conversion systemgenerates a plurality of analog reference signals corresponding to aplurality of digital input signals. The multi-channel conversion systemalso generates an analog multi-carrier signal and samples themulti-carrier signal, where the multi-carrier signal represents a summedamplification of the digital input signals. The correlating powerdetection system is connected to the multi-channel conversion system andgenerates digital total power control signals based on the analogreference signals and the analog sampled multi-carrier signal. Thefeedback conversion module is connected to the multi-channel conversionsystem and the correlating power detection system and individuallycontrols amplification of the digital input signals based on the totalpower control signals.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects, features, and advantages of the present inventionwill become apparent from the following description and the appendedclaims when taken in connection with the accompanying drawings, wherein:

FIG. 1 is a block diagram of an analog-based power control system inaccordance with a preferred embodiment of the present invention; and

FIG. 2 is a block diagram of an analog-based power control system inaccordance with an alternative embodiment of the present invention;

FIG. 3 is a block diagram of a digital-based power control system inaccordance with a preferred embodiment of the present invention;

FIG. 4 is a block diagram of a digital-based power control system inaccordance with an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

1. Analog-based Power Control System

FIG. 1 shows a preferred analog-based power control system 10 for amulti-carrier transmitter in accordance with the present invention.Generally, the power control system 10 provides a base stationtransmitter with the ability to individually control the transmittedpower level of each carrier signal to a high degree of accuracy. Whilethe preferred embodiment is described with respect to a cellular basestation transmitter, the present invention is readily applicable to anytype of multi-carrier transmitter. It can be seen that control system 10has a multi-channel amplification system 20, a correlating powerdetection system 60, and an adjustment module 90. While the preferredcontrol system 10 is shown to have a four-channel capacity, the controlsystem 10 can be readily modified to accept a larger or smaller numberof channels without parting from the spirit and scope of the invention.The multi-channel amplification system 20 converts a plurality of analoginput signals corresponding to channels 1 through 4 into a plurality ofamplified carrier signals. The amplification system 20 also generates aplurality of reference signals corresponding to the amplified carriersignals. This can be done by tapping a small amount of power fromreference points 21, 22, 23, and 24. The amplification system 20 furthergenerates a sampled multi-carrier signal, where the multi-carrier signalincludes a summation of the amplified carrier signals. The sampledmulti-carrier signal can be obtained by tapping a small amount of powerfrom summation point 32.

The correlating power detection system 60 is connected to theamplification system 20, and generates total power control signals basedon the reference signals and the sampled multi-carrier signal. Theadjustment module 90 is connected to the amplification system 20 and thepower detection system 60, and controls amplification of the carriersignals based on the total power control signals. Thus, the presentinvention provides a unique shared architecture for individuallycontrolling the transmitted power of individual carrier signals. Such anapproach significantly improves overall power control and reduces theoccurrence of saturation.

It is important to note that the term “connected” is used herein forease of discussion and is not used in the physical sense per se. Thus,the connections described can be of an electrical, optical, orelectromagnetic nature, or can be any other suitable mechanism fortransferring the signal in question. The detection and control signalsmay be represented in analog or digitally.

2. Multi-channel Amplification System

It will be appreciated that a number of approaches can be taken toimplementing the above-described components. For example, the preferredamplification system 20 has a modulator 25 corresponding to each inputsignal, where the modulators 25 encode the input signals in accordancewith a predetermined modulation protocol. Example protocols includeQPSK, QAM, GMSK, CDMA, and TDMA. The present invention is therefore notlimited to any particular protocol, and can be used in a wide range ofwireless or other multi-channel transmit applications. A multiplier 26is connected to each modulator 25 and a local oscillator 27. Themultipliers 26 multiply the encoded input signals by frequencyconversion signals to move the encoded input signals to desiredfrequencies. This results in the generation of the carrier signals. Forexample, a typical input signal of a few megahertz might be“up-converted” to an approximately 1820 MHz carrier signal with a signalbandwidth of 200 kHz.

It can be seen that an amplifier 28 is connected to each multiplier 26for amplifying the carrier signals, and a voltage-controlled attenuator29 is preferably connected to each amplifier 28 and to the adjustmentmodule 90. The attenuator 29 attenuates the amplified carrier signalbased on an attenuation control signal 35 from the adjustment module 90.It is important to note that the attenuator 29 can be replaced by avariable gain amplifier for the same purpose. In such a case, a gaincontrol signal would be appropriate as a control mechanism. A summationmodule 30 is connected to the attenuators 29 for summing the amplifiedcarrier signals, and a multi-channel power amplifier 31 is connected tothe summation module 30. The multi-channel power amplifier 31 amplifiesthe multi-carrier signal. It is preferred that the amplification system20 further includes a plurality of reference amplifiers 33, and asummation amplifier 34. The reference amplifiers 33 amplify thereference signals to desired levels and the summation amplifier 34amplifies the sampled multi-carrier signal to a desired level.

3. Correlating Power Detection System

As already noted, the correlating power detection system 60 generatestotal power control signals based on the reference signals and thesampled multi-carrier signal. The correlating power detection system 60may either be made up of a switching system 62 and a correlating powerdetector 64 (FIG. 1), or a plurality of correlating power detectors 64,where each power detector 64 corresponds to one of the reference signals(FIG. 2). The alternative analog-based power control system 10′ will bedescribed later. FIG. 1 demonstrates the approach of using a switchingsystem 62.

With continuing reference to FIG. 1, the preferred switching system 62will now be described. Specifically, it can be seen that the switchingsystem 62 is connected to the multi-channel amplification system 20 forselecting an active reference signal from the plurality of referencesignals. Thus, the active reference signal in FIG. 1 corresponds to thecarrier signal for Channel 1. The switching system 62 has a timingcontroller 61 for generating a switching signal, and a switchingmechanism 63 connected to the multi-channel amplification system 20, thecorrelating power detector 64, and the timing controller 61. Theswitching mechanism selects the active reference signal based on theswitching signal, and can be any number of commercially availabledevices well known in the art.

The correlating power detector 64 is connected to the switching system62 and the multi-channel amplification system 20. The power detector 64generates each total power control signal based on the active referencesignal and the multi-carrier signal. In the preferred embodiment, thepower detector 64 has a power limiter 65 connected to the switchingsystem 62 for setting a fixed power level of the active referencesignal. The main purpose of this is to improve the comparison functionto be described below.

An I/Q detector 66 is connected to the limiter 65 and the multi-channelamplification system 20. It is important to note that the activereference signal will contain both phase and frequency information. Thephase information results from the modulation activities describedabove. The frequency information similarly results from theup-conversion described above. The I/Q detector 66 therefore generatesan in phase power signal and a quadrature power signal based on theactive reference signal and the multi-carrier signal. It is important tonote that any power in the multi-carrier signal and the active referencesignal having the same frequency will be a direct current (DC) componentof the in phase and in quadrature power signals. Thus, for the exampleillustrated in FIG. 1, the power signals will have a DC componentcorresponding to the power transmitting on Channel 1.

Thus, a low pass filter 68 can be connected to the I/Q detector 66 forfiltering the unwanted frequencies from the power signals such that DCpower signals result. One DC power signal corresponds to the in phasepower and the other DC power signal corresponds to the quadrature power.Preferably, a summing amplifier 67 is connected to the low pass filter68 for combining the DC power signals. Specifically, the summingamplifier 67 squares, sums, and integrates the DC power signals toobtain the total power control signals. Each total power control signalrepresents the transmitted power level for the selected channel. It willbe appreciated that an operational amplifier can also be used for thispurpose. In fact, these functions can be performed digitally as well asin analog. In such a case, the summing amplifier 67 would be replaced byan A/D converter and commercially available digital signal processingcircuitry well known in the industry.

FIG. 2 demonstrates that in the alternative embodiment of providing apower detector 64 for each one of the reference signals (i.e. channels),the power detectors 64 will be directly connected to the multi-channelamplification system 20.

4. Adjustment Module

Returning now to FIG. 1, it can be seen that the preferred adjustmentmodule 90 has a plurality of sample and hold circuits 92 for storing thetotal power control signals based on a switching signal from thecorrelating power detection system 60. Control circuitry 94 generatesattenuation control signals 35 based on the total power control signalsand predetermined power data. This power data will essentially includeinformation linking desired power levels to transmitted power levels forvarious frequencies. The control circuitry 94 can be implemented withlookup tables, automatic gain control loops, or any other controlmechanism capable of generating either a gain or an attenuation signalbased on the power data. It can also be seen that the control circuitry94 may also include a temperature sensing device such as thermistor 96for generating a temperature signal based on a temperature of thecorrelating power detection system. Specifically, the multipliers in theI/Q detector 66 may be temperature dependent. In this case, the controlcircuitry 94 also generates the attenuation control signals 35 based onthe temperature signal from the thermistor 96.

As shown in FIG. 2, it will further be appreciated that where thecorrelating power detection system 60 includes a plurality of detectors64, the power in each channel is continuously monitored and theadjustment module 90′ does not require sample and hold circuits. Theadjustment module 90′ therefore merely includes the plurality of controlcircuitry 94 and the thermistor 96, if desired.

5. Digital-based Power Control System

It is important to note that while the above-described power controlsystems 10 and 10′ are geared towards analog input signals, it may benecessary to process digital input signals. The digital input signalsinclude channel frequency, power level, and other digital data necessaryfor transmission. Thus, FIGS. 3 and 4 describe a preferred digital-basedpower control system 100, and an alternative digital-based power controlsystem 100′.

With continuing reference to FIG. 3, it can be seen that the powercontrol system 100 has a multi-channel conversion system 110 forgenerating a plurality of analog reference signals corresponding to aplurality of digital input signals. The multi-channel conversion system110 further generates an analog multi-carrier signal and samples themulti-carrier signal. The multi-carrier signal represents a summedamplification of the digital input signals. A correlating powerdetection system 60 is connected to the multi-channel conversion system110 and generates total power control signals based on the referencesignals and the sampled multi-carrier signal. The control system 100also includes a feedback conversion module 120 connected to themulti-channel conversion system 110 and the correlating power detectionsystem 60. The feedback conversion module 120 individually controlsamplification of the digital input signals based on the total powercontrol signals from the correlating power detection system 60.

6. Multi-channel Conversion System

It will be appreciated that a number approaches can be taken toimplementing the above-described components. For example, themulti-channel conversion system 110 can provide the reference signals tothe correlating power detection system 60 serially (as shown in FIG. 3),or in parallel (as shown in FIG. 4). With continuing reference to FIG.3, it can be seen that a digital summer 111 digitally amplifies theinput signals based on a digital attenuation (or gain) control signal.The digital summer 111 also sums the amplified digital input signals togenerate a digital multi-carrier signal. A multi-carrier A/D converter112 is coupled to the digital summer 111 for converting the digitalmulti-carrier signal into a multi-carrier pulse stream. The preferredconverter 112 is a delta sigma converter that generates a pulse widthmodulated bit stream. A multi-carrier filter 113 is connected to themulti-carrier A/D converter 112 for converting the multi-carrier pulsestream into the analog multi-carrier signal. The filter 113 ispreferably a bandpass filter having the desired center frequency andbandwidth.

The preferred multi-channel conversion system 110 further includes achannel selection module 114 for selecting an active input signal fromthe plurality of digital input signals. A single carrier D/A converter115 is coupled to the channel selection module 114 for converting theactive input signal into an active reference pulse stream. Thisconverter 115 is also preferably a delta sigma converter. The conversionsystem 110 further includes a single carrier filter 116 connected to thesingle carrier D/A converter 115 for converting the active referencepulse stream into an active analog reference signal. This signal can beused by the correlating power detection system 60 in measuring thetransmitted power as described in the above analog-based discussion.

Turning now to FIG. 4, the alternative digital-based power controlsystem 100′ is shown. It can be seen that the control system 100′ isvery similar to the one shown in FIG. 3, except for the number of numberof single carrier D/A converters 115 and single channel filters 116, andthe lack of a channel selection module 114. Specifically, FIG. 4demonstrates that a plurality of single carrier D/A converters 115,corresponding to the plurality of digital input signals, convert thedigital input signals into a plurality of reference pulse streams. Aplurality of single carrier filters 116 are therefore connected to thesingle carrier D/A converters 115 for converting the reference pulsestreams into analog reference signals. While this approach requires morecomponents, certain processing advantages may be obtained by eliminatingthe channel selection module 114 (FIG. 3).

7. Feedback Conversion Module

It will also be appreciated that the feedback conversion module 120 canbe implemented in a number of different ways. For example, FIG. 3demonstrates that if the correlating power detection system 60 generatesthe total power control signals serially, the feedback conversion module120 will include an A/D converter 122, and a digital level correctionmodule 124. Specifically, the A/D converter 122 is connected to thecorrelation power detection system 60 for converting the total powercontrol signals into digital feedback signals. The digital levelcorrection module 124 is coupled to the A/D converter for generatingdigital control signals based on the digital feedback signals andpredetermined power data.

As discussed above, the feedback conversion module 122 can furtherinclude a temperature sensing device such as thermistor 126 forgenerating a temperature signal based on a temperature of thecorrelating power detection system 60. In such a case, the digital levelcorrection module further generates the digital control signals based onthe temperature signal.

Turning now to FIG. 4, an alternative feedback conversion module 120′ isshown. Specifically, it can be seen that the correlating power detectionsystem 60 generates the total power control signals in parallel. Thus,the feedback conversion module 120′ has a plurality of A/D converters122 and a digital level correction module 124. The A/D converters areconnected to the correlating power detection system 60 for convertingthe total power control signals into feedback signals. As describedabove, the digital level correction module 124 is coupled to the A/Dconverters for generating digital control signals based on the digitalfeedback signals and predetermined power data. The feedback conversionmodule 120 may also include the thermistor 26 as already discussed.

The present invention therefore allows individual RF carrier levels tobe recovered via I/Q downconverting the multi-carrier spectrum either inparallel or serially by mixing the multi-carrier output with theindividual carriers. It is important to note that the individualcarriers can be either modulated or unmodulated. This provides theability to individually control and monitor the power of an arbitrarynumber of RF carriers in a multi-carrier transmitter. Such a system willbe useful in next generation cellular basestation products and providereduced complexity and costs.

What is claimed is:
 1. A power control system for a multi-carriertransmitter, the power control system comprising: a multi-channelconversion system for generating a plurality of analog reference signalscorresponding to a plurality of digital input signals, the conversionsystem further generating an analog multi-carrier signal and samplingthe analog multi-carrier signal, where the analog multi-carrier signalrepresents a summed amplification of the digital input signals; acorrelating power detection system connected to the multi-channelconversion system, the correlating power detection system generatingtotal power control signals based on the analog reference signals andthe sampled analog multi-carrier signal; and a feedback conversionmodule connected to the multi-channel conversion system and thecorrelating power detection system, the feedback conversion moduleindividually controlling amplification of the digital input signalsbased on the total power control signals.
 2. The control system of claim1 wherein the multi-channel conversion system includes: a digital summerfor digitally amplifying the input signals based on a digital controlsignal, the digital summer further summing the amplified digital inputsignals to generate a digital multi-carrier signal; a multi-carrieranalog to digital (A/D) converter coupled to the digital summer forconverting the digital multi-carrier signal into a multi-carrier pulsestream; a multi-carrier filter connected to the multi-carrier A/Dconverter for converting the multi-carrier pulse stream into the analogmulti-carrier signal; a channel selection module for selecting an activeinput signal from the plurality of digital input signals; a singlecarrier D/A converter coupled to the channel selection module forconverting the active input signal into an active reference pulsestream; and a single carrier filter connected to the single carrier D/Aconverter for converting the active reference pulse stream into anactive analog reference signal.
 3. The control system of claim 2 whereinthe D/A converters include delta sigma converters.
 4. The control systemof claim 1 wherein the multi-channel conversion system includes: adigital summer for digitally amplifying the input signals based on adigital control signal, the digital summer further summing the amplifieddigital input signals to generate a digital multi-carrier signal; amulti-carrier analog to digital (A/D) converter coupled to the digitalsummer for converting the digital multi-carrier signal into amulti-carrier pulse stream; a multi-carrier filter connected to themulti-carrier A/D converter for converting the multi-carrier pulsestream into the analog multi-carrier signal; a plurality of singlecarrier D/A converters corresponding to the plurality of digital inputsignals, the single carrier D/A converters converting the digital inputsignals into a plurality of reference pulse streams; and a plurality ofsingle carrier filters connected to the single carrier D/A convertersfor converting the reference pulse streams into analog referencesignals.
 5. The control system of claim 4 wherein the D/A convertersinclude delta sigma converters.
 6. The power control system of claim 1wherein the multi-channel conversion system selects an active inputsignal from the plurality of digital input signals and generates anactive analog reference signal based on the active input signal, thecorrelating power detection system including a correlating powerdetector connected to the multi-channel conversion system for generatinga total power control signal based on the active analog reference signaland the sampled analog multi-carrier signal.
 7. The power control systemof claim 6 wherein the correlating power detector includes; a limiterconnected to the multi-channel conversion system for setting a fixedpower level of the active analog reference signal; an I/Q detectorconnected to the limiter and the multi-channel conversion system, theI/Q detector generating an in phase power signal and an in quadraturepower signal based on the active analog reference signal and the sampledanalog multi-carrier signal; a low pass filter connected to the I/Qdetector for filtering predetermined frequencies from the power signalssuch that direct current power signals result; and a summing amplifierfor converting the direct current power signals into the total powercontrol signal.
 8. The power control system of claim 1 wherein thecorrelating power detection system includes: a plurality of correlatingpower detectors connected to the multi-channel conversion system forgenerating total power control signals based on the analog referencesignals and the sampled analog multi-carrier signals; each said powerdetector corresponding to one of the analog reference signals.
 9. Thepower control system of claim 8 wherein each correlating power detectorincludes: a limiter connected to the multi-channel conversion system forsetting a fixed power level of the corresponding analog referencesignal; an I/Q detector connected to the limiter and the multi-channelamplification system, the I/Q detector generating an in phase powersignal and an in quadrature power signal based on the correspondinganalog reference signal the sampled analog multi-carrier signal; a lowpass filter connected to the I/Q detector for filtering predeterminedfrequencies from the power signals such that a direct current powersignals result; and a summing amplifier for converting the directcurrent power signals into the total power control signal.
 10. Thecontrol system of claim 1 wherein correlating power detection systemgenerates the total power control signals serially, the feedbackconversion module including: an analog to digital (A/D) converterconnected to the correlating power detection system for converting thetotal power control signals into digital feedback signals; and a digitallevel correction module coupled to the A/D converter for generatingdigital control signals based on the digital feedback signals andpredetermined power data.
 11. The control system of claim 10 wherein thefeedback conversion module further includes a temperature sensing devicefor generating a temperature signal based on a temperature of thecorrelating power detection system, the digital level correction modulefurther generating the digital control signals based on the temperaturesignal.
 12. The control system of claim 1 wherein the correlating powerdetection system generates the total power control signals in parallel,the feedback conversion module including: a plurality of analog todigital (A/D) converters connected to the correlating power detectionsystem for converting the total power control signals into digitalfeedback signals; and a digital level correction module coupled to theA/D converters for generating digital control signals based on thedigital feedback signals and predetermined power data.
 13. The controlsystem of claim 12 wherein the feedback conversion module furtherincludes a temperature sensing device for generating a temperaturesignal based on a temperature of the correlating power detection system,the digital level correction module further generating the digitalcontrol signals based on the temperature signal.